---------- Forwarded message --------- From: Kuee k1r0a <liulin063@xxxxxxxxx> Date: Mon, Aug 8, 2022 at 11:11 PM Subject: Re: [PATCH bpf] bpf: Do more tight ALU bounds tracking To: Daniel Borkmann <daniel@xxxxxxxxxxxxx> On Mon, Aug 8, 2022 at 9:25 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > > On 7/30/22 12:48 AM, Hao Luo wrote: > > On Fri, Jul 29, 2022 at 3:43 PM Youlin Li <liulin063@xxxxxxxxx> wrote: > >> > >> In adjust_scalar_min_max_vals(), let 32bit bounds learn from 64bit bounds > >> to get more tight bounds tracking. Similar operation can be found in > >> reg_set_min_max(). > >> > >> Also, we can now fold reg_bounds_sync() into zext_32_to_64(). > >> > >> Before: > >> > >> func#0 @0 > >> 0: R1=ctx(off=0,imm=0) R10=fp0 > >> 0: (b7) r0 = 0 ; R0_w=0 > >> 1: (b7) r1 = 0 ; R1_w=0 > >> 2: (87) r1 = -r1 ; R1_w=scalar() > >> 3: (87) r1 = -r1 ; R1_w=scalar() > >> 4: (c7) r1 s>>= 63 ; R1_w=scalar(smin=-1,smax=0) > >> 5: (07) r1 += 2 ; R1_w=scalar(umin=1,umax=2,var_off=(0x0; 0xffffffff)) <--- [*] > >> 6: (95) exit > >> > >> It can be seen that even if the 64bit bounds is clear here, the 32bit > >> bounds is still in the state of 'UNKNOWN'. > >> > >> After: > >> > >> func#0 @0 > >> 0: R1=ctx(off=0,imm=0) R10=fp0 > >> 0: (b7) r0 = 0 ; R0_w=0 > >> 1: (b7) r1 = 0 ; R1_w=0 > >> 2: (87) r1 = -r1 ; R1_w=scalar() > >> 3: (87) r1 = -r1 ; R1_w=scalar() > >> 4: (c7) r1 s>>= 63 ; R1_w=scalar(smin=-1,smax=0) > >> 5: (07) r1 += 2 ; R1_w=scalar(umin=1,umax=2,var_off=(0x0; 0x3)) <--- [*] > >> 6: (95) exit > >> > >> Signed-off-by: Youlin Li <liulin063@xxxxxxxxx> > > > > Looks good to me. Thanks Youlin. > > > > Acked-by: Hao Luo <haoluo@xxxxxxxxxx> > > Thanks Youlin! Looks like the patch breaks CI [0] e.g.: > > #142/p bounds check after truncation of non-boundary-crossing range FAIL > Failed to load prog 'Permission denied'! > invalid access to map value, value_size=8 off=16777215 size=1 > R0 max value is outside of the allowed memory range > verification time 296 usec > stack depth 8 > processed 15 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0 > > Please take a look. Also it would be great to add a test_verifier selftest to > assert above case from commit log against future changes. > > Thanks, > Daniel > > [0] https://github.com/kernel-patches/bpf/runs/7696324041?check_suite_focus=true This test case fails because the 32bit boundary information is lost after the 11th instruction is executed: Before: 11: (07) r1 += 2147483647 ; R1_w=scalar(umin=70866960383,umax=70866960638,var_off=(0x1000000000; 0xffffffff),u32_min=2147483647,u32_max=-2147483394) After: 11: (07) r1 += 2147483647 ; R1_w=scalar(umin=70866960383,umax=70866960638,var_off=(0x1000000000; 0xffffffff)) This may be because, in previous versions of the code, when __reg_combine_64_into_32() was called, the 32bit boundary was completely deduced from the 64bit boundary, so there was a call to __mark_reg32_unbounded() in __reg_combine_64_into_32(). But now, before adjust_scalar_min_max_vals() calls __reg_combine_64_into_32() , the 32bit bounds are already calculated to some extent, and __mark_reg32_unbounded() will eliminate these information. Simply copying a code without __mark_reg32_unbounded() should work, perhaps it would be more elegant to introduce a flag into __reg_combine_64_into_32()? Sorry for not completing the tests because I did not 'make selftests' successfully, and uploaded the code that caused the error.
